On the chemistry of creatinine detection via oxaziridine intermediate

In this communication the chemistry of the interaction of creatinine with mercuric cyanide in alkaline medium is described. The separation of elemental mercury is idoneous for a chemical test and also is a hint of what is happening at least in one step. The separation of mercury was taken in advantage by Snapp for his test. Its chemistry is as follows: a hydroxide is added to the imino group present in one of the two tautomeric forms of creatinine. After hydrion transfer an amino group and an alkoxide are formed. The last ion reacts with mercury cyanide eliminating a cyanide ion. The resultant organometallic intermediate is prone to cyclisation because besides the electrodotic effect of the amino group, the δ─ in the cyano group produces a δ+ in the mercury atom. The last two joined effects facilitate the withdrawal of cyanide ion and elemental mercury, this being equivalent to a good leaving group which is necessary for oxaziridine formation (imine oxide). Finally, isomerisation via ring opening of the oxaziridine gives 2-hydoxylamino-creatinine.